The present invention relates to a hair-care composition comprising as film-forming agent an aqueous polymer dispersion, and to the use of such a dispersion in a hair-care composition.
It is known to use aqueous polymer dispersions as film-forming agent in hair-care compositions. The properties of the aqueous dispersions thus obtained depend on the nature of the polymers, and thus of the monomers, from which they are prepared. However, it may be of advantage to be able to modify slightly these properties, for example by accentuating/optimizing a particularly advantageous property or by developing a new property which the said dispersion would not have on the basis of its inherent composition.
An object of the invention is to provide a hair-care composition comprising an aqueous dispersion of a polymer chosen from the group consisting of polyesters, polyesteramides and alkyds which has properties which are improved relative to the polyester, polyesteramide and/or alkyd dispersions of the prior art.
Another object of the invention is therefore a hair-care composition comprising an aqueous polymer dispersion consisting of particles resulting from the free-radical polymerization of at least one radical monomer in the interior and/or partially at the surface of already existing particles of at least one polymer chosen from the group consisting of polyesters, polyesteramides and alkyds. Still another object of the invention is the use of an aqueous polymer dispersion consisting of particles resulting from the free-radical polymerization of at least one radical monomer in the interior and/or partially at the surface of already existing particles of at least one polymer chosen from the group consisting of polyesters, polyesteramides and alkyds as film-forming agent in a hair-care composition.
In the rest of the present description, xe2x80x9cpolyesterxe2x80x9d is understood to mean any polymer, alone or as a mixture, chosen from the group consisting of polyesters, polyesteramides and alkyds.
It has been found that the use in hair-care compositions of aqueous dispersions according to the invention, i.e. of aqueous dispersions of hybrid polyester polymers, makes it possible to obtain a composition which has particular properties, properties which it is not possible to obtain by using, for example, a simple mixture of existing aqueous dispersions of polyester and of acrylic and/or vinyl polymer.
One advantage of the present invention is therefore to be able, on the basis of an already existing aqueous polymer dispersion, to develop and/or optimize certain particularly advantageous properties in a relatively controlled manner.
In preparing the hair-care composition according to the invention, an aqueous polyester dispersion is prepared first of all. This dispersion may be prepared by the person skilled in the art on the basis of their general technical knowledge, in particular as follows. When the polyester polymer is insoluble in water, it is possible to dissolve it in an organic solvent which is slightly soluble in water, to add water so as form an emulsion, then to evaporate the organic solvent so as to give an aqueous dispersion of the polyester polymer in water, having a solids content of approximately 30-50% by weight. When the polyester polymer is autodispersible in water, this step may be omitted if the polymer has a sufficient content of hydrophilic groups.
The aqueous polyester dispersion which is used may be an aqueous dispersion of anionic, cationic, non-ionic or amphoteric polyester, of polyesterarnides, or of alkyds, i.e. of fatty-chain polyesters, individually or in a mixture. The dispersion may also be a dispersion of polyesters with ionizable side groups, such as sulpho or carboxyl groups. The polyester may contain unsaturated groups, for example when it is obtained by polycondensation of a diol or a diamine with an unsaturated acid anhydride, for example maleic anhydride. In this case the charge of the free-radical monomer may react subsequently with the unsaturated polyester and may give rise to grafting and/or to crosslinking. In this way a dispersion of a grafted and/or crosslinked hybrid polymer is obtained, which may, following application of the dispersion, impart to the film obtained particular mechanical properties, such as an improvement in the adhesion of the said film.
The aqueous dispersion of hybrid polyester polymers according to the invention is obtained by free-radical polymerization of at least one monomer in the interior and/or partially at the surface of already existing polyester particles.
The radical monomer may be vinyl or acrylic in nature and may be anionic, cationic, non-ionic or amphoteric. It is also possible to use a mixture of monomers of different kinds. The monomer or monomer mixture is preferably insoluble or slightly soluble in water. Among the monomers which may be employed, it is possible to mention esters or acrylic or methacrylic acid, such as methyl, ethyl, propyl, butyl, isobutyl, tert-butyl and 2-ethylhexyl acrylate or methacrylate; N-substituted or N,N-substituted acrylamides or methacrylamides; vinyl esters such as vinyl acetate; and styrene. It is also possible to use, individually or in a mixture, a vinyl, acrylic or methacrylic monomer comprising one or more siloxane groups, in particular
the monomer of formula
CH2xe2x95x90C(CH3)xe2x80x94C(O)xe2x80x94Oxe2x80x94(CH2)3xe2x80x94Sixe2x80x94[Oxe2x80x94Si(CH3)3]3 
asilicon-containing macromonomer with a monofunctional vinyl, allyl, methacrylic or acrylic acid ester, ether or amide end group, of formula
CH2xe2x95x90C(R1)xe2x80x94C(O)xe2x80x94Xxe2x80x94(CH2)xe2x80x94[Si(CH3)(R4)xe2x80x94Oxe2x80x94]nxe2x80x94Si(CH3)2xe2x80x94R3
in which R1 represents H or CH3, X represents O or NH, p is an integer which may be zero, R3 and R4 independently represent CH3 or an aliphatic, cycloaliphatic or aromatic group, and n is an integer which is preferably between 3 and 300. It is also possible to use a vinyl or allyl monomer or a methacrylic or acrylic acid ester, ether or amide monomer containing one or more halogenated groups, especially chlorinated and/or fluorinated groups, and/or containing a group which absorbs in UVA and/or UVB and which is able to provide, after polymerization, a certain photoprotection against ultraviolet radiation, especially solar radiation, for example substituted or unsubstituted benzylidenecamphor and benzotriazole groups, among which 2-(2xe2x80x2-hydroxy-5-methacryloyloxyethylphenyl)-2H-benzotriazole may be mentioned.
When the monomer or monomer mixture is in liquid form at room temperature, the free-radical polymerization may be carried out without employing a solvent. When the monomer or monomer mixture is in solid form at room temperature, it may be dissolved before the polymerization, preferably in an organic solvent, for example a polar and water-miscible solvent such as methanol. In this case, after polymerization, it is possible to distil off the organic solvent present in the aqueous dispersion, if necessary.
The aqueous dispersions according to the invention are prepared under conditions such that the monomer polymerizes in the interior and/or partially at the surface of the polymer particles without any nucleation, i.e. without the formation of new particles. To achieve this, the polyester polymer in aqueous dispersion having a solids content of 30-50% by weight may be introduced into a polymerization reactor. It is then possible to add to this reactor the monomer or monomer mixture, as it is or in solution in an appropriate solvent, and a free-radical polymerization initiator.
Depending on what kind it is, the free-radical initiator is introduced in the form of a solution in an organic solvent, in the form of an aqueous solution, or else dissolved beforehand in the monomer mixture. In the first case, it may be added at the same time as the monomer in solution, and in the second case it may be added after the monomer. An organic free-radical polymerization initiator which is not soluble in water may be used, of the peroxide or percarbonate type, such as tert-butyl, peroxy-2-ethylhexanoate, or a water-soluble organic initiator, or else an inorganic initiator such as potassium persulphate.
An aqueous mixture is thus prepared which comprises the polyester polymer, the monomer and the polymerization initiator. It is also possible to add to this mixture a stabilizer which may be, in particular, a surfactant or a mixture of surfactants which is or are anionic, amphoteric, cationic and/or non-ionic. When the polyester used is itself ionic, it is preferred to use a surfactant of the same ionic or amphoteric kind. It is preferred to use an ionic, polyoxyethylenated surfactant in a quantity of 0.5-10% by weight of solids, relative to the weight of polyester solids. The mixture is then heated to the required temperature so as to allow the decomposition of the initiator, and polymerization is continued until the monomers have been consumed.
The proportions of radical monomer to polyester polymer may be 10-95% by weight of radical monomer solids and 5-90% by weight of polyester solids.
An aqueous dispersion of hybrid polymer is thus obtained whose constituent particles are present in the form of composite particles, similar to an xe2x80x9calloyxe2x80x9d of the two base polymers and with a size comparable with that of the polyester particles before free-radical polymerization. The dispersions thus obtained possess characteristic properties which are different from those which would be obtained by mixing two aqueous dispersions of each of the constituents.
The dispersions according to the invention may be used as film-forming agent in hair-care compositions such as lacquers or shampoos, hair-setting lotions, styling lotions or mousses, in the same way as an aqueous polymer dispersion according to the state of the art. These compositions comprise the ingredients which are conventionally employed in the hair-care field, and may be prepared according to the usual methods which are known to the person skilled in the art. It is also possible to use the dispersions according to the invention in products which are intended for the photoprotection of hair against ultraviolet radiation, in particular against solar radiation, when they contain an appropriate monomer which is capable of providing a certain sun protection.